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What is a Topographic Survey?

Posted 03.09.18

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A topographic survey (or land survey) is an exercise undertaken by land surveyors who use a rapidly expanding array of survey equipment to capture spatial data about an area of land and it's use. Relating measurements back to fixed coordinates, sufficient points (measurements) are recorded to reproduce the natural and artificial topographical features on a 2D and/or 3D map,plan or model. 

The end result all depends on what the survey is for and how the end users intend to interact with the survey data. The position and ground level of topographic features are usually displayed, with supporting height information on overhead features such as roofs, trees and cables. Boundaries and surfaces are annotated and contours may be displayed to assist with visualising the 3d element of the terrain when working with a 2d drawing. Historically, the results of the survey were delivered manually drawn or printed/plotted onto a physical medium. Due to the minimum possible thickness of a line when printing, the requested scale of the drawing dictated the level of detail and accuracy of the survey.

Now we can scroll our mouse wheel and zoom in and the line doesn't get any thicker on our screen. We can click two buttons and all the existing buildings will disappear but a background map from 25 years ago will be displayed instead, or a 3d model of something new. Paper plans are now used as a prop for site walkovers and meetings whilst the drawings are delivered digitally and worked with by a range of professions within the property and construction industry. Either in a 2D or 3D CAD (Computer Aided Design) environment or as a PDF, set up to replicate a traditional paper plan when printed.

A view of a 2D survey file in CAD software with the Layers window visible.

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A view of a 3D topographic survey file in CAD software with 3D Faces (triangles shown). A 3D points file (CSV) can also be supplied for Revit compatibility.

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A PDF plot of a survey from a CAD file. This is set up to replicate a paper plan and will print/plot to the specified scale when printed correctly.

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High precision, real time GPS/GNSS equipment and total stations have been the go-to tools for surveyors producing land survey deliverables such as these. But the advent of rapid data collection systems such as terrestrial laser scanning and drone photogrammetry provides new possibilities. Conventional line and level data can be extracted from the massive point clouds and imagery generated by these methods. Furthermore the point cloud can be further processed to be used in BIM (Building Information Modelling) projects or delivered with a free standalone 3D viewer software package which allows users to view, measure and interrogate the model.

We are very pleased to work with Aspect Air Solutions in the provision of drone photogrammetry services. Aspect Air is part of GNA Surveyors, a long established firm of Chartered Surveyors. Using only pilots who are also RICS chartered, this ensures highly qualified and experienced staff oversee the data acquisition, ground control and data processing elements of a project.

View of a textured 3d model produced with drone photogrammetry methods.

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A view of the underpinning point cloud data used in the example above.

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This technique offers extremely efficient data collection on large areas of open terrain and is usually deployed for stock pile surveys, quarry surveys, post demolition surveys and a wide array of inspection and progress reporting tasks.

Topographic surveys are typically used by architects, engineers and designers. Having one carried out at an early stage of a project is generally the recommended advice and a well specified survey can be instrumental for other professions consulting on a project and in for-seeing potential issues. Physical boundaries are a routine feature to survey within a land survey area and if the area specified is extended to the approximate area indicated by the title plan, a simple overlay of the two data sets can be performed.


This title plan overlay showed a triangular portion of the intended development land, not being included within the title (roughly outlined in blue)

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Land Registry make no requirement to represent the legal boundary on a title plan and as such very few examples exist. Instead a general boundary is shown usually as a thick red line. This triangle of unregistered land was identified through a comparison between the physical boundary from a topographic survey and an overlay of the title plan. Despite the ambiguity surrounding the accuracy of Ordnance Survey data and the general boundary lines derived from it, this area is significant enough to warrant a bit of housekeeping with land registry at an early stage - as this "slither" of unregistered land is key to securing safe access into and out of a proposed development.

The topographic survey data can be used in a 3d environment to model sight lines for visibility splays when assessing viability to move or create an access from an existing highway. Parameters vary by speed limit and authorities but taking into account the parameters for required line of sight distance at a specific position and eye level, the driver's line of sight can be modelled to address planning concerns. In this example, the removal of an outgrown hedge and replacement with a 0.9m ht highway boundary treatment made all the difference.

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Flood risk assessments may call for a topographic survey to be undertaken to enable modelling of watercourses and flood plains. These are commonly carried out to Environment Agency specifications for watercourse channels and structures, or the client may provide their own specification.

3D digital terrain model with water level timetabling. Animated videos showing site conditions at a range of theoretical water table levels can be produced.

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For full fluvial/hydraulic/flood modelling tasks, water course cross sections are likely to be required. Water course survey data can be delivered as cad drawings/pdf's or in specialist flood modelling software formats.Watercourse cross section
The process of gathering fit for purpose survey data and processing it into usable outputs varies according to the survey specification and end user requirements. For example, a "post-demolition" survey is a topographic survey with a focus on the volumes of different materials formed in stock piles, the finished ground levels across the site and the change between old and new within the site area. It can be suitable to tie the survey into the control of an existing topographic survey so that when volumes are calculated, undulations in the terrain at the base of the stock piles can be accounted for.

Once the new land use has been designed and approved it's time for setting out. Many contractors employ a full time site engineer who is responsible for setting out the new buildings, roads, drainage etc. In some cases site engineers do not have access to equipment required or lack the skill set specific to setting out. Topographical staff are trained, qualified and insured to complete setting out tasks for our clients. Setting out is like accurately recording the position of a very important point on the ground, to display on a computer or plan, except in reverse. The coordinates for the new roads, buildings, drainage etc should be available within the design drawings, correctly referenced to the topographic survey used in producing the designs. The appropriate equipment, markers and techniques must be selected to accurately place (set out) a marker either on a coordinate or relating to it - depending upon the construction technique being applied. The accuracy of the set-out coordinate must be checked in real time and verified against other set out points and survey control. To contribute fully to a project when site engineering, requires knowledge and experience of ground work, civil engineering and construction techniques and can lead to a greater emphasis on problem solving and collaborating with stakeholders on site.

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As built surveys rely on the same, topographic survey techniques - to transfer the measured position of all the new features, back into a digital file for analysis against the design drawings (the intended coordinates). Supplementary plans can be generated for Section 38  and Section 278 works which will usually have to meet the specific guidelines of the authority in question. Laser scanners can be utilised to update BIM models or to provide high resolution surface modelling possibilities which provide robust and comprehensive flatness and vertical checks.

To discuss your land survey or site engineering requirements with Topographical, please don't hesitate to call 01158 497 685, email surveys@topographical.co.uk or click here to use our interactive quote tool (please provide as much information as possible).


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